1. Field of the Invention
The present invention relates to a prepreg using a thermosetting resin composition having excellent moldability and excellent heat resistance and flame resistance, and a laminate and a metal-foil-clad laminate each of which uses the above prepreg.
2. Description of Prior Art
As a printed wiring board material for electronic equipment, there are widely used a prepreg using an epoxy resin or BT (bismaleimide/triazine) resin composition, a laminate obtained by curing the above prepreg under heat, and a multilayer board using a combination of the above laminate and the above prepreg. As a method for imparting flame retardancy to these printed wiring board materials, there is generally adopted a recipe containing a bromine type compound. In recent years, however, a variety of regulations for bromine type flame retardants are discussed in view of environmental issues and combinations of various flame-retardant compounds are studied for the purpose of producing a halogen-free material.
In addition, a lead-free solder is coming to be used in place of a conventional lead solder at the time of mounting electronic parts. In accordance with the above, it is unavoidable that a temperature at the time of solder reflow increases by 20 to 30° C. Therefore, a printed wiring board material which can endure a high reflow temperature and is excellent in solder heat resistance, becomes indispensable. It is strongly desired to develop a halogen-free material which is excellent in solder heat resistance and is environmentally friendly.
For the above movements, for example, as for an epoxy resin-based printed wiring board material, various halogen-free flame retardants are studied for aiming to delete brominated epoxy resins. The mainstream of currently-proposed examples is a method using a compound containing phosphorus or nitrogen in combination with aluminum hydroxide. However, since aluminum hydroxide starts to undergo a dehydration reaction at approximately 200° C., there is a limitation in regard to solder heat resistance.
As a means to improve the heat resistance of aluminum hydroxide, there is disclosed a method in which aluminum hydroxide is partially dehydrated by heating to decrease the apparent number of moles of a crystallization water to 1.8–2.9 (JP-A-51-27898). When such aluminum hydroxide is added to a thermosetting resin, irregularities occur on a molded appearance due to an influence of pores caused by the thermal dehydration treatment. Therefore, it is difficult to apply the above aluminum hydroxide to a general printed wiring board material.
Currently, concerning a halogen-free flame-retardant printed wiring board material using an epoxy resin of a BT resin as a base material, there is generally adopted a method using aluminum hydroxide as a flame retardant concurrently. However, aluminum hydroxide itself is insufficient in heat resistance, and a laminate obtained by incorporating it in a thermosetting resin has a limitation in solder heat resistance. There is hardly found a halogen-free flame-retardant printed wiring board material having solder heat resistance applicable to a lead-free solder which requires a temperature higher than a conventional temperature.